* * * * * But by far the most prominent object upon the plateau was the enormous gleaming thing that Helen had said was the station over which came the signals from the Master Intelligence on Mars. One of its three towers sprang up not far from where he stood. The huge, refulgent ring, swathed in its mist of purple fire, was a full hundred feet above him; and the slender needle, pulsing with white flame, swinging within and below the colossal ring, was itself a hundred feet in length. The white needle, for all its length, seemed hardly thicker than a man's finger. It was mounted at the top of a curiously complex and delicate-looking device that spread broadly out between the three towers, below the center of the huge purple ring. Dan looked at it and decided that his plan had at least a chance of success--though he had no hope that it would not be fatal to him. Quickly and silently he ran to the base of the mighty silver towers nearest him and began to climb the side toward the ravine, where the maze of girders would hide him, at least partially, from any watchers back on the plateau. The starlight and the faint weird radiance of the purple ring above sufficed to guide him. The cross-braces on the girder he had chosen were spaced closely enough to serve as the rungs of a ladder. Dan climbed easily, pausing twice for breath, and to look down at the dark plateau. The vast, humming machines loomed up strangely in the pale purple light that fell from the gleaming ring. Once he looked across toward the other side of the island. The surface there was more level. He glimpsed tiny moving lights, and huge stationary masses, apparently as large as ocean liners. He had an impression of a vast amount of mechanical activity, proceeding in the darkness very rapidly, and in a silent and orderly fashion. "The expeditionary force of the Master Intelligence of Mars," he thought, "preparing to set out against humanity! And what I can do is the only chance to stop it!" * * * * * He climbed again with renewed energy. A few yards more brought him to the colossal metal ring. Resting upon the three towers, it was a circular band of shining metal a foot thick and as wide as a road. The intense purple glow extended several feet from its surface. Dan touched it tentatively. He felt a tingling electric shock. And he thought he could feel a radiation coming from it, giving him a curious sensation of cold. As he reached his hands up and grasped the upper edge of the great ring, he felt what seemed a physical current of cold. Controlling his tendency to shiver, he climbed upon the last brace, and, lifting his weight with his hands, threw himself face down upon the flat upper surface of the vast ring. He lay bathed in cold purple fire. He tingled with the chill of it. A frozen current seemed to penetrate his body. Involuntarily he trembled, lost his grip and dangled precariously from the rim.